1. Field of the Invention
My invention relates to characterizing the surface of a papermaking fabric. In specific examples, my invention relates to apparatuses, processes, and systems for determining the characteristics of the contact surface of a fabric that is used for three-dimensional structuring of a web in a papermaking process.
2. Related Art
In processes of forming paper products, such as tissue paper and paper towels, three-dimensional shaping is conducted while the papermaking web is still highly deformable, i.e., when the papermaking web has a high water content. Often, this three-dimensional shaping of the web is conducted on a woven structuring fabric. The fabric provides a contact surface made up of knuckles in the yarns of the fabric, with pockets being formed in the fabric between the knuckles. When the papermaking web is applied to the fabric, portions of the web contact the knuckles, and other portions of the web are drawn into the pockets. Before being removed from the fabric, the web is dried to a point such that its shape is fixed or locked. Domes are thereby formed in the dried web where the web was drawn into the pockets in the fabric, and the domes are present in the finished paper product. Hence, the paper product has a distinct three-dimensional structure formed, in part, by the knuckle and pocket characteristics of the structuring fabric.
Because the contact surface of a structuring fabric directly relates to the shape of the finished product, the choice of a structuring fabric is often based on the shape of the product that is desired. It is difficult, however, to characterize the contact surface of a structuring fabric based on a simple visual inspection of the fabric. While the knuckles of the fabric can easily be seen, it is often difficult to accurately determine the sizes of the knuckles, difficult to determine the areas of the pockets between the knuckles, and difficult to determine the depth of the pockets into which the papermaking web is drawn during the papermaking process. As such, there have been previous techniques that attempt to quantify the characteristics of the contact surface of the fabric, for example, using formulas based on the yarn parameters of the fabric. It has been found, however, that such formulas are often not accurate enough to characterize the contact surface of the fabric in a manner that allows for an accurate prediction of the paper product structure that will be formed with the fabric. Additionally, the contact area characteristics will often change as the fabric is run on a papermaking machine. For example, wear on the surface of the fabric will generally increase the lengths of the knuckles, thereby changing the structuring that will be imparted on the web by the fabric. Thus, formulas for determining the contact surface characteristics that are applicable to initial fabric configurations will not necessarily apply to fabrics that have become worn over time.
It would be beneficial, therefore, to provide a technique for accurately characterizing the contact area characteristics of a structuring fabric that is used in a papermaking process. Moreover, it would be beneficial to provide a technique that can easily determine the contact area characteristics as the fabric becomes worn, over time, while the fabric is mounted on a papermaking machine.